Experts then said conspiracy theorists were likely to seize on any delay as evidence the government is dead set on keeping the truth about aliens away from the public.

The Rendlesham Forest incident: Britain’s most famous UFO sighting

The Rendlesham Forest incident took place in December 1980 over several nights.
On December 26, 1980, military personnel at the twin bases of RAF Bentwaters and RAF Woodbridge in Suffolk saw a strange light in Rendlesham Forest, which lies between the two bases.

Three men were sent out to investigate and two of them encountered a small, triangular-shaped craft.

One man, Jim Penniston, got close enough to touch the side of the object.

He and another of the airmen present, John Burroughs, made sketches of the craft for witness statements

Two nights later Deputy Base Commander, Lieutenant Colonel Charles Halt and his team then encountered the UFO.

He said later: “Here I am, a senior official who routinely denies this sort of thing and diligently works to debunk them, and I’m involved in the middle of something I can’t explain.”

A UFO trail sign at Rendlesham Forest, which has become a hotspot for alien hunters

However, the National Archive told us that it was simply following rules forbidding the publication of certain sensitive documents during a period of “purdah” ahead of the General Election.

Nick Pope, an expert who worked as the Ministry of Defence’s UFO investigator for 15 years, said: “As a former civil servant I completely understand the reasons for this, but the UFO community will be up in arms and this is bound to start more conspiracy theories,” he said.

“When I made the official announcement of the declassification and release of these UFO files in May 2008, it was believed the release project would take two or three years.

“Now, more than nine years later, there’s a danger that what started as a good news story about open government and freedom of information is turning into a public relations disaster.

“I hope the release of the last files can be fast-tracked after the election.”

MOST READ IN TECH AND SCIENCE

SPRING CLEAN

WATCH OUT

BEAT THE HACKERS

Follow these tips to make sure you're NEVER an online fraud victim again

TERROR TRIALS

How Soviet scientists created 'humanzees', two-headed dogs and poison chamber

STAR PLAYER

10 celebrities you never realised were massive video game nerds

SCRAP BOOK

How to delete your Facebook account after 'data breach' hits 50 million users

It’s hoped the files will relate to an incident dubbed the British Roswell, which took place in Rendlesham Forest over three nights between 26 and 28 December, in 1980.

Military personnel from nearby RAF Bentwaters and RAF Woodbridge, including the deputy base commander, witnessed strange lights in the forest and saw them hovering above the twin NATO airbases, which were on high alert as the Cold War was at its peak.

Three men were sent out to investigate and two of them encountered a small, triangular-shaped craft.

Last year, an American airman involved in the incident won a legal bid to force military health chiefs to pay for the treatment of injuries he claimed to have sustained at Rendlesham Forest.

“In citing the [MoD radiation documents] and in granting John Burroughs full disability for his injuries in Rendlesham Forest, the US Government has by de facto acknowledged the existence of unidentified aerial phenomena which, in John Burroughs’ case, resulted in physical injury,” his lawyer Pat Frascogna said.

We pay for your stories! Do you have a story for The Sun Online news team? Email us at tips@the-sun.co.uk or call 0207 782 4368